tencent cloud

Suggestions for Dealing with Exceptions

If exceptional errors occur when you call KMS APIs to send requests from your application to the remote KMS server, you can deal with the errors as suggested below:

• Cancel the call: if an error shows that the failure is not temporary and persists after several re-executions, you need to terminate or cancel the application call and report the error.
• Try again immediately: if an uncommon error is returned, for example, network packets are damaged during transfer but still sent, in this case, you can try again immediately.
• Increase delays between re-executions: if an error is generally caused by connections, it indicates that the server is busy and needs to clear the loads first. You can try again in a while in such cases.

The following paragraphs introduce how to increase delays between re-executions. The delay can be gradually increased or scheduled (by implementing exponential backoff). As the frequency of KMS API calls is limited, you can increase delays between re-executions to avoid errors caused by high frequency.

Exponential Backoff

Pseudocode

// Gradually increase re-execution delays
InitDelayValue = 100
For(Retries = 0; Retries < MAX_RETRIES; Retries = Retries+1)
        wait for (2^Retries * InitDelayValue) milliseconds
        Status = KmsApiRequest()
        IF Status == SUCCESS
            BREAK // Succeeded, stop calling the API again.
        ELSE IF Status = THROTTLED || Status == SERVER_NOT_READY
            CONTINUE // Failed due to throttling or server busy, try again.
        ELSE
            BREAK // another error occurs, stop calling the API again.
        END IF

Method

Python: implement exponential backoff for frequency errors in KMS API calls to Encrypt

# -*- coding: utf-8 -*-
import base64
import math
import time
from tencentcloud.common import credential
from tencentcloud.common.exception.tencent_cloud_sdk_exception import TencentCloudSDKException
from tencentcloud.common.profile.client_profile import ClientProfile
from tencentcloud.common.profile.http_profile import HttpProfile
from tencentcloud.kms.v20190118 import kms_client, models


def KmsInit(region="ap-guangzhou", secretId="", secretKey=""):
          try:
                credProfile = credential.Credential(secretId, secretKey)
                client = kms_client.KmsClient(credProfile, region)
                return client
          except TencentCloudSDKException as err:
                print(err)
                return None
                
def BackoffFunction(RetryCount):
            InitDelayValue = 100
            DelayTime = math.pow(2, RetryCount) * InitDelayValue
            return DelayTime
            
if __name__ == '__main__':
            # User-defined parameters
            secretId = "replace-with-real-secretId"
            secretKey = "replace-with-real-secretKey"
            region = "ap-guangzhou"
            keyId = "replace-with-realkeyid"
            plaintext = "abcdefg123456789abcdefg123456789abcdefg"
            Retries = 0
            MaxRetries = 10
            client = KmsInit(region, secretId, secretKey)
            req = models.EncryptRequest()
            req.KeyId = keyId
            req.Plaintext = base64.b64encode(plaintext)
            while Retries < MaxRetries:
                try:
                    Retries += 1
                    rsp = client.Encrypt(req)  # Call the API `Encrypt`
                    print 'plaintext: ',plaintext,'CiphertextBlob: ',rsp.CiphertextBlob
                    break
                except TencentCloudSDKException as err:
                    if err.code == 'InternalError' or err.code == 'RequestLimitExceeded':
                        if Retries == MaxRetries: 
                            break
                        time.sleep(BackoffFunction(Retries + 1))
                        continue
                    else:
                        print(err)
                        break
                except Exception as err:
                    print(err)
                    break

Note：

• To deal with other specific errors, you can directly modify the content of the statement except.
• You can customize the schedule policy based on your code logic and business policy to set the optimal initial delay value (InitDelayValue) and the number of retries (Retries), preventing your business from being affected by a too-low or too-high threshold.